HTTP sent to the debug RPC port produces a misleading RPC size-limit warning #7705

Description

Sending an HTTP request to workerd’s debug RPC port produces incoming RPC message exceeds size limit, with a calculated size of tens of billions of words.

The actual input is only a 115-byte HTTP request. This can occur when local development tools probe listening TCP ports to discover HTTP servers.

Environment

• workerd: 1.20260811.1
• OS: WSL2 Linux x86_64

Steps to reproduce

Create config.capnp:

using Workerd = import "/workerd/workerd.capnp";

const config :Workerd.Config = (
  services = [(name = "main", worker = (
    compatibilityDate = "2026-08-11",
    modules = [(name = "worker.js", esModule =
      "export default { fetch() { return new Response('ok'); } };"
    )]
  ))],
  sockets = [(name = "http", address = "127.0.0.1:14655", http = (), service = "main")]
);

Start workerd:

workerd serve --debug-port=127.0.0.1:14656 config.capnp

Send an HTTP request to the RPC port:

curl --http1.1 \
  --header 'User-Agent: Go-http-client/1.1' \
  --header 'Connection: close' \
  --header 'Accept-Encoding: gzip' \
  --header 'Accept:' \
  http://127.0.0.1:14656/

Actual behavior

The connection is closed, and workerd logs:

NOSENTRY RPC connection broken for non-DISCONNECTED reason.
capnp/serialize-async.c++:789: failed:
expected expectedSizeInWords <= options.traversalLimitInWords
[36753147483 <= 8388608]; incoming RPC message exceeds size limit

The HTTP Worker on port 14655 remains responsive.

Expected behavior

Could this input be rejected with a clearer invalid-message or protocol-mismatch diagnostic?

The current warning suggests an oversized RPC transfer or an internal RPC failure, even though the input is a small HTTP request sent to the wrong port.